In the 1970s, new tests using tube agglutination were introduced. These ring tests used prepackaged red blood cells to detect HCG. However, they were abandoned due to sensitivity to motion. Modern pregnancy tests use monoclonal antibodies to detect HCG. Even minute amounts of HCG can bind to the antibodies, allowing pregnancy to be detected six days after conception. Still, the phrase is used, but the rabbits are bit happier with the way things are now.